The clubs have agreed to quit the existing structures and establish a new mid-week competition, the Super League, in an apparent grab for more money and power.
The 12 foundation clubs are Premier League giants Arsenal, Chelsea, Liverpool, Manchester City, Manchester United and Tottenham; La Liga heavyweights Atletico Madrid, Barcelona and Real Madrid; and Serie A trio AC Milan, Inter Milan and Juventus.
No German or French clubs have signed up.
The league plans to launch "as soon as practicable" and the founding clubs will be given 3.5 billion euros ($A5.4b) "to support their infrastructure investment plans and to offset the impact of the COVID pandemic" a statement from the Super League said.
The Super League organisers anticipate three more teams to join as founding members with five more to qualify annually for a 20-team competition.
The format of the competition would be two groups of 10 playing home and away fixtures with the top three in each group qualifying for the quarter-finals.
A play-off involving fourth and fifth placed teams will complete the final eight, before home-and-away knockout rounds until a single fixture final at a neutral venue.
A women's Super League competition is also planned to be launched after the men's league is up and running, the statement said.
Real Madrid president Florentino Perez is the founding chairman of the Super League, with Manchester United co-chairman Joel Glazer and Juventus chairman Andrea Agnelli the vice-chairmen.
"We will help football at every level and take it to its rightful place in the world," Perez said.
Football is the only global sport in the world with more than four billion fans and our responsibility as big clubs is to respond to their desires.
The Super League statement said clubs do not feel UEFA's proposed changes to the Champions League - which are due to be confirmed on Monday with an expansion to 36 teams from 32 - go far enough.
It added the 12 clubs would now seek to work with UEFA and world governing body FIFA to "deliver the best outcomes for the new League and for football as a whole".
FIFA and UEFA condemned the plans, with Europe's governing body saying it would ban any club involved from playing in its domestic league.
The Super League has also been heavily criticised by other soccer authorities, UK Prime Minister Boris Johnson and French President Emmanuel Macron.